The present invention relates to ducts for gas turbine engines, and more particularly to configurations of mid-turbine frame ducts for gas turbine engines.
In some gas turbine engines, a mid-turbine frame is utilized between turbine stages, such as between a high-pressure turbine (HPT) stage and a low-pressure turbine (LPT) stage. The mid-turbine frame includes a vane that guides combustion gases as they pass through the duct. The vane can comprise or envelop a strut that provides engine structural support that can be used, for instance, to connect the gas turbine engine to an aircraft. In some gas turbine engines, a flowpath radial offset is desired, with the radial offset initiated as close as possible downstream of the HPT blades. In order to provide such a radial offset, an annular duct formed at the mid-turbine frame induces a radial offset of combustion gases passing between the HPT and LPT stages, that is, an increase in radius in the downstream direction.
A problem encountered with mid-turbine frames is the tendency for the radial offset of the duct to cause flow diffusion. Flow diffusion can cause combustion gas flow in the duct to separate from boundary wall surfaces of the duct, causing fluid mixing and relatively high aerodynamic losses. It is desirable to reduce such flow separation and reduce aerodynamic losses.